Background information

Environmental risks of biological control

Reducing the risk

It must be accepted that the risk of adverse impacts from biological control
releases can probably never be eliminated. However, carefully conceived
containment or quarantine studies can almost certainly reduce risk.
Protocols for host
specificity testing of weed biological control agents have been developed which
depend upon a system of 'centrifugal phylogenetic testing' (Wapshere 1974).
This means that non-target species from those most closely related to the target
weed to those more distantly related are exposed in sequence to the proposed
biological control agent. This enables a profile of the host range of the
organism to be developed and facilitates the decision on whether or not to
proceed with field release. With insects, assembling a suitable list of
potential non-target species to be tested is more difficult because of the much
larger number of species involved, and the lack of precise taxonomic
information. However, the principles of the system used for weed biological
control agents can to some extent be extended to insects.

There has been considerable debate about the desirability of host specificity in
proposed biological control agents. While some contend that the presence of
alternative hosts can assist the biological control agent through periods when
the target host is scarce (Nechols et al. 1992), others maintain that it is
irresponsible to release any biological control agent unless it can be
demonstrated to be completely host specific. Then again, it is argued that
laboratory tests can be unreliable because in confinement in an artificial
environment, some proposed biological control agents attack species that would
not be attacked in the field (Sands 1993) and vice versa. There is still
a great deal of research that needs to be carried out to underpin the design of
reliable and feasible protocols. A possible approach is to verify the
pre-release predictions of host range made from laboratory tests with
post-release field studies to determine realised
host range in the field (Barratt et al. 1997). This can help to build up a database
which can assist decision makers in the future.
Clearly, the environmental risks associated with the
introduction of a biological control agent have to be weighed against the economic benefits of
controlling a pest, or in some cases, the environmental cost of doing nothing.